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					Synthetic Fiber Creation



      “Spinning”
Fiber
overview




Spring 2001   ISAT 430   Dr. Ken Lewis               2
                                         Module 3A
Plan of attack
 Synthetic Fiber History
 Spinning Fundamentals
       Nomenclature
       Things Common To All
   Basic methods of spinning a fiber
       Melt spinning
       Wet spinning
       Dry spinning
   Some details of Lycra® spandex formation

Spring 2001             ISAT 430   Dr. Ken Lewis               3
                                                   Module 3A
Fibers -- History

   Textiles predate recorded history
       fabrics were made thousand of years before written
        records
   All early fibers were from animals or plants
       wool -- sheep      shrinks
       silk -- silk worms      delicate
       cotton -- cotton plant wrinkles
       linen -- flax plant wrinkles
   All had problems...
Spring 2001             ISAT 430   Dr. Ken Lewis               4
                                                   Module 3A
Fibers -- History2

   1664
        Robert Hooke predicted artificial silk
        Nothing happened.
   1855
        Swiss chemist Audemars received first patent for
         artificial silk
             dissolved the inner bark of a mulberry tree and made
              cellulose
        Nothing happened.

Spring 2001                 ISAT 430   Dr. Ken Lewis                 5
                                                       Module 3A
Fibers -- History3

   1910
        First commercial rayon
   1938
        Nylon
   1959
        Lycra® spandex
   1974
        Kevlar® aramid

Spring 2001               ISAT 430   Dr. Ken Lewis               6
                                                     Module 3A
Nomenclature
   Spinning

       Fiber users
             To mingle and make a continuous yarn from staple fibers
              (like spinning wool into yarn)

       Fiber makers
             To extrude and make a fiber in continuous form (much
              like a spider spins her silk)


   Today --- we are spiders.
Spring 2001                 ISAT 430   Dr. Ken Lewis                    7
                                                       Module 3A
                                          Wool
Nomenclature                       up to 20 inches long
                                          Staple

   Staple
        short fibers
                                    Silk
   Filament                up to 450 yards long
        long fibers              Filament


         Cotton
    1 - 2 inches long
          Staple                          All synthetic Fibers
                                                Filament

Spring 2001             ISAT 430   Dr. Ken Lewis                 8
                                                   Module 3A
Nomenclature2

   Denier
      A measure of the fineness of a yarn
      Denier = grams / 9000 meters
      Linear density
      Allows comparison of yarns of different densities
           wool
           cotton
           nylon
           etc.


Spring 2001            ISAT 430   Dr. Ken Lewis               9
                                                  Module 3A
Nomenclature3

   Tenacity
        A measure of the strength of a fiber.
        Measured as: Grams force / denier


   Elongation
        How much a fiber can be stretched before it breaks.
        Measured as percent.



Spring 2001              ISAT 430   Dr. Ken Lewis               10
                                                    Module 3A
Spinnability               Hydrodynamic instability




Jet distortion
& growth

                                                           Cohesive
                                                           fracture




        Spinnable

Spring 2001         ISAT 430   Dr. Ken Lewis                          11
                                               Module 3A
Spinnability continued
   Let  be any scalar variable of interest
             (denier, yarn temperature, solvent concentration…)


                           
                                        0
                           t   x,y,z




            The fiber is evolving but at any particular point in space
             it does not change with time.
            Spinning implies steady state

Spring 2001                 ISAT 430    Dr. Ken Lewis               12
                                                        Module 3A
                               
      • However:      grad      0
                               z



      • That is, the fiber is changing as it moves down the
        cell.




Spring 2001            ISAT 430   Dr. Ken Lewis               13
                                                  Module 3A
Spinning
 Fiber formation conditions are carefully controlled
 Essentials
           Start with a melted polymer or polymer/solvent solution
           Extrude this liquid through one or more small orifices
            called spinneret capillaries
           Perform the necessary transport processes
                – May be heat transfer, mass transfer, chemical reactions or
                  a combination of all.
                – The more precise control of these variables the more
                  uniform the fiber
             Wind up the finished fiber

Spring 2001                  ISAT 430   Dr. Ken Lewis                      14
                                                        Module 3A
Spinning2
   Piece of cake!


   Except….
       The solvent may be toxic, corrosive, or explosive
       The temperatures may be in the 300 - 400 ºC range
       The fiber residence time from extrusion to cell exit may
        range from seconds to milliseconds.


Spring 2001             ISAT 430   Dr. Ken Lewis               15
                                                   Module 3A
Things Common to all Spinning

           Even
          Crylex®
         has these!!          Spinnerets

      Metering Pumps                          Spin Cells



Spring 2001        ISAT 430   Dr. Ken Lewis                16
                                               Module 3A
Spin Cell
          Polymer solution                    Essentially the cell
              or melt in                       provides control and
                                               containment.
                                              Control
                                                   temperature
                                                   fiber components
The Cell                                      Contain
                                                   Fluids
                                                      Solvents
                                                      Gases
                                                   Toxins

              Filaments out
Spring 2001                   ISAT 430   Dr. Ken Lewis                 17
                                                         Module 3A
Metering Pumps
                    Sit at the top of the cell
                    Deliver precisely the
                     correct amount of polymer
                     to the spinneret.
                    Positive Displacement
                     pumps
                    Can be single stream or
                     many streams
                    Allow precise control of
                     the filament size (denier)
                                         Spinneret

                               Like a shower head
                               Holes are called
                                capillaries.
                               Depending on the process
                                    8 capillaries up to 1000
                                     capillaries




Spring 2001   ISAT 430   Dr. Ken Lewis                          19
                                           Module 3A
The Spinneret
                               Function
                                    Converts the polymeric
                                     liquid from a homogeneous
                                     mass into discrete filaments
                                    Controls the molecular
                                     alignment of the polymer
                                     molecules
                                    Imparts shear energy into
                                     the system from the shear
                                     stresses in the capillaries.
                                        These are critical



Spring 2001   ISAT 430   Dr. Ken Lewis                         20
                                          Module 3A
Spin Cell Assembly
                                              Metering pump
                                             & polymer supply

   Spinneret




   Spin Cell
                                          filaments




Spring 2001    ISAT 430   Dr. Ken Lewis                     22
                                             Module 3A
Examples
        Example         Method
                 
         Lycra            Dry

         Nylon            Melt
                 
        Dacron            Melt

         Rayon            Wet
                                              Later we will
                 
        Nomex          Dry, Wet              examine a few
                 
        Kevlar        Wet (airgap)           in some detail
        Acrylic           Dry

         Glass            Melt
                 
        Tyvex          Dry (flash)


Spring 2001          ISAT 430    Dr. Ken Lewis                23
                                                 Module 3A
Melt Spinning
Melt Spinning

 Not the oldest spinning method
 More straight forward
        removal of heat
        no solvents to worry about.


   Example -- nylon



Spring 2001              ISAT 430   Dr. Ken Lewis               25
                                                    Module 3A
Nylon
                              +
     Hexamethylamine                         Adipic acid




                Nylon 6, 6
Spring 2001            ISAT 430   Dr. Ken Lewis               26
                                                  Module 3A
                   
Nylon                    Either cross flow or radial gas flow.
                             staple yarn uses radial
                             filament yarn uses crossflow
                        Uniformity of the air flow is critical
                        Minimum air necessary is used to
                         reduce turbulence.
                        Three forces resist the feed roll
                             Resistive inertial
                             Rheological stresses
                             Aerodynamic or drag forces
                              (important for spinning speeds >
                              5000 m/min
Spring 2001   ISAT 430    Dr. Ken Lewis                          27
                                           Module 3A
Wet Spinning
Wet Spinning
   If a polymer
       does not melt
       dissolves only in non-volatile or thermally unstable
        solvents
 We wet spin
 Polymer solution is extruded into a liquid bath
       miscible with the solvent
       does not solvate the polymer.
   Example:      Kevlar®
Spring 2001              ISAT 430   Dr. Ken Lewis               29
                                                    Module 3A
    Kevlar®


    Kevlar® is intractable and
     insoluble
          except in 100+ wt % H2SO4
          which is miscible in H2O.


    PPD-T / H2SO4 becomes
     liquid crystalline in
     concentrations above 12%
          Shear stress then aligns the
           molecules.


    Spring 2001                  ISAT 430   Dr. Ken Lewis               30
                                                            Module 3A
Kevlar®       Viscosity
                                  Isotropic solution
                                   produces amorphous low
                                   strength filaments

                                  anisotropic solution
                                   produces Kevlar®



                              The concrete wall

Spring 2001      ISAT 430   Dr. Ken Lewis                 31
                                            Module 3A
Kevlar®            Spinning

   Traditional wet spinning did not work
      As soon as the solution exited the spinneret, it
       coagulated.
      It would not draw
      Remained low strength, and friable



   Then in 1970 Herb Blades made a mistake
        He left the spinneret in air!


Spring 2001               ISAT 430   Dr. Ken Lewis               32
                                                     Module 3A
Kevlar®           Air Gap Spinning
         Metering pump                              Spinneret




                                                             To drying and
 4 ºC water                                                  constant
                                                             tension winder




   Neutralization &
   Washing bath

Spring 2001              ISAT 430   Dr. Ken Lewis                             33
                                                        Module 3A
The Air Gap
                               Difference between
                                success and failure.
                                    Allows the molecules to
                                     align
                                    almost no further draw once
                                     the filament hit the water.


                               A 2” diameter spinneret
                                may extrude 1000
                                filaments at once.


Spring 2001   ISAT 430   Dr. Ken Lewis                        34
                                          Module 3A
Dry Spinning
Dry Spinning

   Some polymers do not melt efficiently
        They may decompose
        The melt viscosity may be too high to process


   May be able to find a low molecular weight
    solvent
        Which allows a reasonable concentration of polymer
        Which has a reasonable volatility


Spring 2001              ISAT 430   Dr. Ken Lewis               36
                                                    Module 3A
 Solution is extruded into a hot gas
 As the filaments pass down the cell, the hot gas
  causes the solvent to vaporize
 This process is complex
       Heat transfer
       Mass transfer
          through the filament
          into the gas
       Gas - solvent management
   Example: Lycra®

Spring 2001               ISAT 430   Dr. Ken Lewis               37
                                                     Module 3A
      Lycra Polymer
                                    +
Poly tetramethylene ether glycol        4,4’-methylenebis(4-phenylisocyanate)




                       Lycra® spandex
      Spring 2001                  ISAT 430   Dr. Ken Lewis                     38
                                                              Module 3A
A word on the gas management
                                   Note what happens
                                    when the volume
                                    percent oxygen > 10%

                                   Kablooie!!!

                                   So careful isolation is
                                    essential
                                            safety
                                            environment

Spring 2001   ISAT 430   Dr. Ken Lewis                        39
                                              Module 3A
                                         Hot Nitrogen (300 - 450 ºC)
                                                  inserted


                           Gas is made uniform
              Polymer is dissolved in
                                      and
              dimethylacetamide (DMAc) and
                                      heats
                          The gaspasses the    solvent,
              then pumped to the top of the cell
                            into passed from the
                          Solutionthe filaments
                              driving it into the
                            spinneret assembly
                                     and
                             extruded into the
                                   filaments.
                                    down
                                  spin cell
                                      the
                                     cell



Spring 2001         ISAT 430   Dr. Ken Lewis                       40
                                               Module 3A
                            Near the bottom of the cell
                             there is a vacuum box.
                                  The solvent rich gas is extracted.
                                  The solvent is recovered.


                           Just at the cell exit
                                 Recycle gas is inserted into the
              Long cell           cell
                                    DMAc >15% flammable
Vacuum                              Keeps solvent/gas from the
Box                                   room
                                    Acts as a curtain
  Recycle
                           The fibers exit the cell and
                            pass to the winders.
Spring 2001      ISAT 430    Dr. Ken Lewis                           41
                                               Module 3A
             The fibers fully formed
              exit the cell.

             Pass to the feed rolls
                  actually pull the yarn from
                   the cell
                  two are used for tension
                   control
             Finish is applied
Feed
             Passes to the winders
rolls



  The
winders
 Lycra® Polymer

      Soft segment              Hard segment
(tetramethylene glycol)   (diisocyanate and ureas)
Lycra®         Polymer

   During polymerization and polymer solution
    transport, the hard segments begin to associate
      in Kevlar ® the liquid crystalline molecules are held
       together with Van der Waal forces
      in Lycra ® hydrogen bonding holds the hard segments
       together




Spring 2001            ISAT 430   Dr. Ken Lewis                44
                                                  Module 3A
Molecular
    Spinneret
Orientation
    Capillary

       Lead in
      Shear rate                          Capillary
      increasing
                                       High Shear rate
                                      High Orientation



    Barus Bulge
  Zero Shear rate
                                       Neck down
Partial deorientation
                                     Elongational Flow
                                     High Orientation


                        To winders
Drying the filaments
     Drying rate limitations
             how fast we can transfer heat into the filaments

                          hD
                 N Nu       • Is the limitation
                           k

         how fast solvent can diffuse through the filament and
          across the surface
         the persistence of the solvent / gas boundary layer.


Spring 2001                    ISAT 430   Dr. Ken Lewis               46
                                                          Module 3A
Yarn Temperature
                               DMAc begins to leave the
                                filament
                               temperature of the
                                filament is restrained by
                                the boiling point of the
                                DMAc.
                               At cell exit, the threadline
                                temperature is ~200 C



Spring 2001   ISAT 430   Dr. Ken Lewis                    47
                                         Module 3A
Yarn Velocity
                              Initially threadline is in
                               freefall

                              During this time of solvent
                               removal tensile force from
                               the feed roll are not
                               transmitted.
                              At solvent levels ~10% the
                               threadline can transmit
                               information and it
                               accelerates up to feed roll
                               speed.

Spring 2001   ISAT 430   Dr. Ken Lewis                      48
                                         Module 3A
Cell limits
     Drying rate limitations
          How fast we can transfer heat into the filaments and
           mass out of the filaments.
              hD
       N Nu      , and DDMAc   • Is the limitation
               k
        How fast solvent can diffuse through the filament and
         across the surface

          The persistence of the solvent / gas boundary layer.


Spring 2001               ISAT 430   Dr. Ken Lewis                49
                                                     Module 3A
              Fiber Tenacities




Spring 2001      ISAT 430   Dr. Ken Lewis               50
                                            Module 3A
              Fiber Elongation




Spring 2001      ISAT 430   Dr. Ken Lewis               51
                                            Module 3A
Fiber
overview




Spring 2001   ISAT 430   Dr. Ken Lewis               52
                                         Module 3A
At long last...

   We have seen the similarities in the different ways
    of manufacturing synthetic fibers

   We have seen some of the difficulties

   And we have seen a little of the beauty of science.



Spring 2001          ISAT 430   Dr. Ken Lewis               53
                                                Module 3A

				
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